Analysis of motion controller requirements for precision planar motion system with parallel kinematics

This paper presents a research of motion controller for a precision air bearing motion stage with parallel kinematics. The air bearing motion stages offers high precision positioning resolution due to frictionless motion, usage of high resolution optical encoders and temperature stable materials. The high resolution processing of current and position feedback as well as linearity of a power stage are critical tasks of precision motion. The research demonstrates that the motion controller requires 14-bit current and position feedback resolution to achieve 5 nm positioning resolution with an application of 20 μm position encoder. An oversampling and a position observer at 20 kHz control frequency could be used to reduce feedback noises. The low current ripples are provided by the H-bridge converter, which controls each motor coil independently. The results were obtained using the enhanced simulation model and the measurement of the motion system prototype, which demonstrates positioning resolution of 22 nm.